This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/JP99/07245 which has an International filing date of Dec. 24, 1999, which designated the United States of America.
1. Technical Field
The present invention relates to a process and an apparatus for producing ketoisophorone derivatives by oxidizing xcex2-isophorone derivatives.
2. Background Technology
Ketoisophorone derivatives [e.g., 2,6,6-trimethylcyclohex-2-ene-1, 4-dione (ketoisophorone, KIP)] are useful intermediates for medicines, pesticides, perfumes, condiments, and polymer resins.
Japanese Patent Application Laid-Open No. 125316/1976 (JP-A-51-125316) discloses a method for producing an ethylenically unsaturated dicarboxylic acid (ketoisophorone) by oxidizing xcex2-ethylenically unsaturated ketone (xcex2-isophorone) with molecular oxygen or a molecular oxygen-containing gas in the presence of an inorganic or organic base and a cobalt or manganese chelate. In this literature, as the solvent, there are enumerated aromatic hydrocarbons, chlorinated aliphatic hydrocarbons, lower aliphatic alcohols, ketones, carboxyamides, nitriles, amines, and ethers.
In Japanese Patent Application Laid-Open No. 53553/1998 (JP-A-10-53553) discloses a method for producing ketoisophorone by oxidizing xcex2-isophorone with molecular oxygen in the presence of a manganese complex salt and an organic base. In this literature, there are disclosed that the oxidation reaction is effected in the presence of water and that an organic acid, such as acetic acid and butyric acid, is added as an additive. Moreover, the use of a ketone (e.g., acetone, methyl isobutyl ketone) or an ether as the solvent is also described.
In these methods, however, certain of bases may sometimes lower the conversion of the substrate or selectivity considerably or cause xcex2-isophorone to isomerize to xcex1-isophorone. Particularly, when the concentration of xcex2-isophorone in the reaction system is high (e.g., 20% by weight or more), the yield of ketoisophorone is significantly reduced. In these methods, if the reaction is repeated or performed continuously with the solvent circulating, high conversions and high selectivities are hardly kept.
xcex2-isophorone can be prepared by isomerizing xcex1-isophorone in the presence of an isomerizing catalyst composed of an acid. For example, in Japanese Patent Publication No. 8650/1979 (JP-B-54-8650) is disclosed a method for producing xcex2-isophorone by the isomerization of xcex1-isophorone in the presence of an isomerizing catalyst (an acid having a pK value of 2 to 5) followed by distillation.
Here, there may be proposed a process of producing ketoisophorone from xcex1-isophorone by combining the isomerizing reaction and oxidizing reaction. The use of xcex2-ketoisophorone obtained by the isomerization of xcex1-isophorone, however, inhibits the oxidation reaction from efficiently proceeding, thus difficulty in producing ketoisophorone continuously.
As a process of producing ketoisophorone from xcex1-isophorone, in Japanese Patent Publication No. 30696/1980 (JP-B-55-30696), Japanese Patent Application Laid-Open No. 191645/1986 (JP-A-61-191645), and Japanese Patent Application Laid-Open No. 93947/1975 (JP-A-50-93947) are disclosed methods of producing 4-oxoisophorone by oxidizing xcex1-isophorone with oxygen in the presence of a catalyst. Japanese Patent Application Laid-Open No. 81347/1974 (JP-A-49-81347) discloses a method for producing 4-oxoisophorone by oxidizing xcex1-isophorone with an alkaline metal chromic acid salt or a dichromate or a chromium trioxide. In the Chem. Lett. (1983), (7), 1081, there is proposed a method of producing 4-oxoisophorone by oxidizing xcex1-isophorone with t-butylhydroperoxide in the presence of a palladium catalyst. However, in these methods, since the selectivity to ketoisophorone is low, separation of the by-product(s) formed or the metal catalyst and purification of the object compound are made complicated. Moreover, these methods sometimes involve the use of a heavy metal compound such as chromium which requires special treatment, or a peroxide which needs to be handled with care, leading to a decrease in working efficiency.
Thus, an object of the present invention is to provide a process and an apparatus for producing ketoisophorone derivatives at high conversions and high selectivities.
Another object of the present invention is to provide a process and an apparatus for continuously and efficiently producing ketoisophorone derivatives even in the case where xcex2-isophorone derivatives obtained from xcex1-isophorone derivatives are employed.
Still another object of the present invention is to provide a process and an apparatus for producing ketoisophorone derivatives without causing a reduction in conversion and selectivity even in the case of performing a reaction continuously with a solvent circulating.
The inventors of the present invention made intensive and extensive studies to achieve the aforementioned objects and found that, in an oxidation reaction of a xcex2-isophorone derivative, an acid component present in the solvent in a very small amount adversely affects the catalyst, considerably deteriorating activity of the catalyst. The present invention is based on the above findings.
Thus, the process for producing ketoisophorone derivatives of the present invention comprises, in the presence of an oxidizing catalyst, oxidizing xcex1-isophorone derivative represented by the following formula (1): 
wherein the groups R1 are the same or different, each representing an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group
in a solvent which contains substantially no acid component to form a ketoisophorone derivative represented by the following formula (2): 
wherein the groups R1 have the same meaning as defined above.
The amount of the acid component in the solvent is about 0 to 4,000 ppm (weight basis), and the solvent may be one treated with an alkali. The acid component is, for example, an organic carboxylic acid. A complex salt of a transition metal and an N,Nxe2x80x2-disalicylidenediamine may be employed as the oxidizing catalyst. Optionally, a cyclic base may be used together as a co-catalyst. The solvent separated from the reaction mixture may be recycled for reuse in oxidizing xcex2-isophorone derivatives after the acid component having been separated therefrom.
The present invention also includes an apparatus for producing ketoisophorone derivatives which comprises a removing unit for removing the acid component in the solvent, and a reactor for forming a ketoisophorone derivative of the formula (2) by, in the presence of an oxidizing catalyst, oxidizing a xcex2-isophorone derivative of the formula (1) in the solvent supplied from the removing unit.